Which of the following has highest `%` enol content in the liquid?

Options

A.
B.
C.
D.

Explanation

To determine which compound has the highest percentage of enol content in the liquid state, we need to analyze the keto-enol tautomerism of each option provided in the question. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Understand Keto-Enol Tautomerism
Keto-enol tautomerism involves the interconversion between a keto form (with a carbonyl group, C=O) and an enol form (with a hydroxyl group, -OH, and a double bond). The stability of the enol form is influenced by factors such as hydrogen bonding and hyperconjugation.

### Step 2: Analyze Each Compound
1. **Compound A**: Contains a keto group with an alpha hydrogen. The enol form can stabilize through hydrogen bonding, but it does not have significant hyperconjugation.

2. **Compound B**: Contains two keto groups, both with alpha hydrogens. The enol form can stabilize through hydrogen bonding and has significant hyperconjugation due to the presence of multiple substituents. This compound is likely to have a higher enol content because of the stability provided by both hydrogen bonding and hyperconjugation.

3. **Compound C**: Similar to Compound B, but the enol form is not stabilized by hydrogen bonding. Although it has alpha hydrogens, the lack of hydrogen bonding means that the enol content will be lower compared to Compound B.

4. **Compound D**: Contains a keto group and an amine. The presence of the lone pair on the nitrogen can participate in resonance, which reduces the tendency for keto-enol tautomerism to occur. Therefore, the enol content will be lower compared to Compound B.

### Step 3: Compare Stability and Enol Content
- **Compound A**: Moderate enol content due to hydrogen bonding but lacks hyperconjugation.
- **Compound B**: Highest enol content due to both hydrogen bonding and hyperconjugation.
- **Compound C**: Lower enol content due to lack of hydrogen bonding.
- **Compound D**: Lowest enol content due to resonance stabilization of the keto form.

### Conclusion
Based on the analysis, **Compound B** has the highest percentage of enol content in the liquid state due to its stability from hydrogen bonding and hyperconjugation.

### Final Answer
**Compound B** has the highest `%` enol content in the liquid.

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